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Journal of Bacteriology, March 2007, p. 1827-1835, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01766-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Growth Phase Regulation of Vibrio cholerae RTX Toxin Export{triangledown}

Bethany Kay Boardman, Brian M. Meehan,{dagger} and Karla J. Fullner Satchell*

Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Tarry 3-713, 303 E. Chicago Avenue, Chicago, Illinois 60611

Received 20 November 2006/ Accepted 13 December 2006

Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, secretes several "accessory" toxins, including RTX toxin, which causes the cross-linking of the actin cytoskeleton. RTX toxin is exported to the extracellular milieu by an atypical type I secretion system (T1SS), and we previously noted that RTX-associated activity is detectable only in supernatant fluids from log phase cultures. Here, we investigate the mechanisms for regulating RTX toxin activity in supernatant fluids. We find that exported proteases are capable of destroying RTX activity and may therefore play a role in the growth phase regulation of toxin activity. We determined that the absence of RTX toxin in stationary-phase culture supernatant fluids is also due to a lack of toxin secretion and not attributable to solely proteolytic degradation. We ascertained that the T1SS apparatus is regulated at the transcriptional level by growth phase control that is independent of quorum sensing, unlike other virulence factors of V. cholerae. Additionally, in stationary-phase cultures, all RTX toxin activity is associated with bacterial membranes or outer membrane vesicles.

* Corresponding author. Mailing address: Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Tarry 3-713, 303 E. Chicago Avenue, Chicago, IL 60611. Phone: (312) 503-2162. Fax: (312) 503-1339. E-mail: k-satchell{at}northwestern.edu.

{triangledown} Published ahead of print on 22 December 2006.

{dagger} Present address: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111.

Journal of Bacteriology, March 2007, p. 1827-1835, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01766-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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